The relief above comes from the pyramid temple of the Old Kingdom Pharaoh Sahure at Abusir, constructed in the mid-third millennium BC. Beneath a text in praise of Sahure, we find the depiction of a boat full of foreigners from the Near East, including one man captioned in hieroglyphs as ‘a’. (The arm sign representing ayin, with a kilt determinative.) This term ‘a’ appears in several forms in ancient Egyptian: ‘Aaa’ (aleph, ayin, ayin) and ‘iaau’ are variants. It comes from a root meaning to ‘babble’ or ‘bray’ like a donkey, and its meaning seems to have been widened to include incomprehensible or foreign speech.
So who are the people marked ‘a’ in the reliefs at Abusir? Opinions vary. They may be Egyptian officials in charge of relations with foreigners. They may be interpreters (Egyptian or foreign). Or – the suggestion which makes most sense to me – people who combined a linguistic role with a more general mediatory one, in trade and diplomacy
The most critical modern discussion of the term is Lanny Bell’s 1976 dissertation on Interpreters and Egyptianized Nubians, available here.